Electromagnetic relay

ABSTRACT

An electromagnetic relay includes a fixed contact, a moving contact, an electromagnet device, and a second coil. The moving contact moves from a closed position where the moving contact is in contact with the fixed contact to an open position where the moving contact is out of contact with the fixed contact, and vice versa. The electromagnet device includes a first coil and a mover. The mover is actuated on receiving a magnetic flux generated when a current flows through the first coil to move the moving contact from one of the closed position or the open position to the other position. The second coil gives, when a current flows through the second coil, at least a magnetic flux, of which a direction is opposite from a direction of the magnetic flux generated by the first coil, to the mover.

TECHNICAL FIELD

The present disclosure generally relates to an electromagnetic relay,and more particularly relates to an electromagnetic relay with theability to turn ON and OFF a pair of contacts.

BACKGROUND ART

Patent Literature 1 discloses an electromagnetic relay for switching theON/OFF states of a current using a pair of contacts. Specifically, theelectromagnetic relay of Patent Literature 1 causes a moving iron core(mover) to move with electromagnetic force generated by energizing anexcitation coil (first coil) of an electromagnet device, thereby movinga moving contactor that a contact device includes. This brings a movingcontact of the moving contactor into contact with a fixed contact of afixed terminal that the contact device includes to connect the fixedterminal and the moving contactor together.

In the electromagnetic relay of Patent Literature 1, the mover is placedin a magnetic field generated by energizing the first coil. Thus, evenwhen the first coil is no longer energized (i.e., no longer has magneticfield), the mover may still remain magnetized (i.e., may have remanentmagnetization).

CITATION LIST Patent Literature

Patent Literature 1: JP 2014-232668 A

SUMMARY OF INVENTION

It is therefore an object of the present disclosure to provide anelectromagnetic relay with the ability to reduce the remanentmagnetization of the mover.

An electromagnetic relay according to an aspect of the presentdisclosure includes a fixed contact, a moving contact, an electromagnetdevice, and a second coil. The moving contact moves from a closedposition where the moving contact is in contact with the fixed contactto an open position where the moving contact is out of contact with thefixed contact, and vice versa. The electromagnet device includes a firstcoil and a mover. The mover is actuated on receiving a magnetic fluxgenerated when a current flows through the first coil to move the movingcontact from one of the closed position or the open position to theother position. The second coil gives, when a current flows through thesecond coil, at least a magnetic flux, of which a direction is oppositefrom a direction of the magnetic flux generated by the first coil, tothe mover.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a schematic configuration for an electromagneticrelay according to an exemplary embodiment of the present disclosure;

FIG. 2 is a cross-sectional view illustrating an OFF state of theelectromagnetic relay;

FIG. 3 is a cross-sectional view illustrating an ON state of theelectromagnetic relay;

FIG. 4 illustrates how the electromagnetic relay operates;

FIG. 5 shows the magnetic properties of a mover in an electromagneticrelay according to a comparative example;

FIG. 6 shows the magnetic properties of a mover in an electromagneticrelay according to the exemplary embodiment of the present disclosure;

FIG. 7 is a cross-sectional view illustrating an OFF state of anelectromagnetic relay according to a first variation of the exemplaryembodiment of the present disclosure;

FIG. 8 is a cross-sectional view illustrating an ON state of theelectromagnetic relay;

FIG. 9 illustrates how the electromagnetic relay operates;

FIG. 10 is a cross-sectional view illustrating an OFF state of anelectromagnetic relay according to a second variation of the exemplaryembodiment of the present disclosure; and

FIG. 11 is a cross-sectional view illustrating an OFF state of anelectromagnetic relay according to a third variation of the exemplaryembodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Note that embodiments and their variations to be described below areonly examples of the present disclosure and should not be construed aslimiting. Rather, those embodiments and variations may be readilymodified in various manners depending on a design choice or any otherfactor without departing from a true spirit and scope of the presentdisclosure. It should also be noted that the drawings to be referred toin the following description of embodiments and their variations are allschematic representations. That is to say, the ratio of the dimensions(including thicknesses) of respective constituent elements illustratedon the drawings does not always reflect their actual dimensional ratio.

(1) Configuration

(1.1) Electromagnetic Relay

An electromagnetic relay 100 according to an exemplary embodimentincludes a contact device 1 and an electromagnet device 10 as shown inFIGS. 1 and 2. The contact device 1 includes a pair of fixed terminals11, 12 and a moving contactor 2. The fixed terminals 11, 12 respectivelyhold fixed contacts 111, 121 thereon. The moving contactor 2 holds apair of moving contacts 21, 22 thereon.

The electromagnet device 10 includes a first coil 101 and a mover 15.The electromagnet device 10 is configured to have the mover 15 attractedby a magnetic field generated by the first coil 101 when the first coil101 is energized. Attracting the mover 15 causes the moving contacts 21,22 held by the moving contactor 2 to move from an open position to aclosed position. As used herein, the “open position” refers to theposition of the moving contacts 21, 22 when the moving contacts 21, 22go out of contact with the fixed contacts 111, 121, respectively. Also,as used herein, the “closed position” refers to the position of themoving contacts 21, 22 when the moving contacts 21, 22 come into contactwith the fixed contacts 111, 121, respectively. That is to say, themoving contacts 21, 22 move from the closed position to the openposition, and vice versa.

In the embodiment to be described below, the electromagnetic relay 100is supposed to be used as a part of onboard equipment for an electricvehicle. In that case, the contact device 1 (fixed terminals 11, 12) iselectrically connected on a path along which DC power is supplied from atraveling battery 61 to a load (such as an inverter) 62.

(1.2) Contact Device

Next, a configuration for the contact device 1 will be described.

As shown in FIGS. 1 and 2, the contact device 1 includes the pair offixed terminals 11, 12, the moving contactor 2, and a container 3. Thefixed terminal 11 holds the fixed contact 111 thereon, and the fixedterminal 12 holds the fixed contact 121 thereon. The moving contactor 2is a plate member made of a metallic material with electricalconductivity. The moving contactor 2 holds a pair of moving contacts 21,22, which are arranged to face the pair of fixed contacts 111, 121,respectively.

In the following description, the direction in which the fixed contacts111, 121 and the moving contacts 21, 22 face each other is definedherein to be an upward/downward direction, and the fixed contacts 111,121 are located on an upper side when viewed from the moving contacts21, 22, just for the sake of convenience. In addition, the direction inwhich the pair of fixed terminals 11, 12 (i.e., the pair of fixedcontact 111, 121) are arranged side by side is defined herein to be arightward/leftward direction, and the fixed terminal 12 is supposed tobe located on the right when viewed from the fixed terminal 11. That isto say, in the following description, the upward, downward, rightward,and leftward directions are supposed to be defined on the basis of thedirections shown in FIG. 2. Furthermore, in the following description,the direction perpendicular to both the upward/downward direction andthe rightward/leftward direction (i.e., the direction coming out of thepaper on which FIG. 2 is depicted) is defined herein to be aforward/backward direction. Note that these directions should not beconstrued as limiting a mode of using the electromagnetic relay 100.

One (first) fixed contact 111 is held at the bottom of one (first) fixedterminal 11, while the other (second) fixed contact 121 is held at thebottom of the other (second) fixed terminal 12.

The pair of fixed terminals 11, 12 are arranged side by side in therightward/leftward direction. Each of the pair of fixed terminals 11, 12is made of an electrically conductive metallic material. The pair offixed terminals 11, 12 serves as terminals for connecting an externalcircuit (including the battery 61 and the load 62) to the pair of fixedcontacts 111, 121. In this embodiment, the fixed terminals 11, 12 aresupposed to be made of copper (Cu), for example. However, this is onlyan example and should not be construed as limiting. Alternatively, thefixed terminals 11, 12 may also be made of any electrically conductivematerial other than copper.

Each of the pair of fixed terminals 11, 12 is formed in the shape of acylinder, of which a cross section, taken along a plane intersectingwith the upward/downward direction at right angles, is circular. Thepair of fixed terminals 11, 12 are each held by the container 3 suchthat part of the fixed terminal 11, 12 protrudes from the upper surfaceof the container 3. Specifically, each of the pair of fixed terminals11, 12 is fixed onto the container 3 so as to run through an opening cutthrough the upper wall of the container 3.

The moving contactor 2 is formed in the shape of a plate havingthickness in the upward/downward direction and having a greaterdimension in the rightward/leftward direction than in theforward/backward direction. The moving contactor 2 is arranged under thepair of fixed terminals 11, 12 such that both longitudinal ends thereof(i.e., both ends thereof in the rightward/leftward direction) face thepair of fixed contacts 111, 121, respectively. Portions, respectivelyfacing the pair of fixed contacts 111, 121, of the moving contactor 2are provided with the pair of moving contacts 21, 22, respectively.

The moving contactor 2 is housed in the container 3. The movingcontactor 2 is moved up and down (i.e., in the upward/downwarddirection) by the electromagnet device 10 arranged under the container3, thus allowing the moving contacts 21, 22 held by the moving contactor2 to move from the closed position to the open position, and vice versa.FIG. 2 illustrates a state where the moving contacts 21, 22 arecurrently located at the open position. In this state, the pair ofmoving contacts 21, 22 held by the moving contactor 2 are out of contactwith their associated fixed contacts 111, 121, respectively. FIG. 3illustrates a state where the moving contacts 21, 22 are currentlylocated at the closed position. In this state, the pair of movingcontacts 21, 22 held by the moving contactor 2 are in contact with theirassociated fixed contacts 111, 121, respectively.

Therefore, when the moving contacts 21, 22 are currently located at theclosed position, the pair of fixed terminals 11, 12 are short-circuitedtogether via the moving contactor 2. That is to say, when the movingcontacts 21, 22 are currently located at the closed position, the movingcontacts 21, 22 come into contact with the fixed contacts 111, 121,respectively, and therefore, the fixed terminal 11 is electricallyconnected to the fixed terminal 12 via the fixed contact 111, the movingcontact 21, the moving contactor 2, the moving contact 22, and the fixedcontact 121. Thus, if the fixed terminal 11 is electrically connected toone member selected from the group consisting of the battery 61 and theload 62 and the fixed terminal 12 is electrically connected to the othermember, the contact device 1 forms a path along which DC power issupplied from the battery 61 to the load 62 while the moving contacts21, 22 are located at the closed position. On the other hand, while themoving contacts 21, 22 are located at the open position, the pair offixed terminals 11, 12 are opened.

In this embodiment, the moving contacts 21, 22 only need to be held bythe moving contactor 2. Therefore, the moving contacts 21, 22 may beformed by hammering out portions of the moving contactor 2, for example,so as to form integral parts of the moving contactor 2. Alternatively,the moving contacts 21, 22 may be members provided separately from themoving contactor 2 and may be secured, by welding, for example, onto themoving contactor 2. Likewise, the fixed contacts 111, 121 only need tobe held by the fixed terminals 11, 12, respectively. Therefore, thefixed contacts 111, 121 may form integral parts of the fixed terminals11, 12, respectively. Alternatively, the fixed contacts 111, 121 may bemembers provided separately from the fixed terminals 11, 12 and may besecured, by welding, for example, onto the fixed terminals 11, 12,respectively.

The container 3 houses the pair of fixed contacts 111, 121 and themoving contactor 2. The container 3 only needs to be formed in the shapeof a box that houses the pair of fixed contacts 111, 121 and the movingcontactor 2. Thus, the container 3 does not have to be formed in theshape of a hollow rectangular parallelepiped as in this embodiment butmay also be formed in the shape of a hollow elliptic cylinder or ahollow polygonal column, for example. That is to say, as used herein,the “box shape” refers to any shape in general which has a space tohouse the pair of fixed contacts 111, 121 and the moving contactor 2inside, and therefore, does not have to be a rectangular parallelepipedshape. The container 3 is formed by joining together a housing, aflange, and an upper plate of a yoke 13 of the electromagnet device 10to be described later. In FIG. 2, the structure of the electromagnetdevice 100 is illustrated in a simplified form and illustration of thehousing, the flange, and the upper plate of the yoke 13 is omitted. Thesame statement applies to FIGS. 3, 7, 8, 10, and 11 as well.

The housing may be made of a ceramic material such as aluminum oxide(alumina). The housing is formed in the shape of a hollow rectangularparallelepiped, of which the dimension is greater in therightward/leftward direction than in the forward/backward direction. Thelower surface of the housing is open. The upper surface of the housinghas a pair of openings to pass the pair of fixed terminals 11, 12therethrough. The pair of openings may be formed in a circular shape,for example, and runs through the upper wall of the housing along thethickness thereof (i.e., in the upward/downward direction). The fixedterminal 11 is passed through one opening and the fixed terminal 12 ispassed through the other opening. The pair of fixed terminals 11, 12 andthe housing are joined together by brazing, for example. Furthermore,the housing does not have to be made of a ceramic material but may alsobe made of an electrical insulating material such as glass or resin ormay even be made of a metallic material. In any case, the housing issuitably made of a non-magnetic material so as not to be magnetized withmagnetism and turn into a magnetic body.

The flange is made of a non-magnetic metallic material, which may be anaustenitic stainless steel such as SUS304. The flange may be formed inthe shape of a hollow rectangular parallelepiped elongated in therightward/leftward direction. The upper and lower surfaces of the flangeare open. The flange is arranged between the housing and theelectromagnet device 10. The flange is hermetically bonded to thehousing and the upper plate of the yoke 13. This turns the internalspace, surrounded with the housing, the flange, and the upper plate ofthe yoke 13, of the contact device 1 into a hermetically sealed space.The flange does not have to be made of a non-magnetic material but mayalso be made of an alloy, such as 42 alloy, including iron as a maincomponent.

(1.3) Electromagnet Device

Next, a configuration for the electromagnet device 10 will be described.

The electromagnet device 10 is arranged under the moving contactor 2 asshown in FIGS. 1 and 2. The electromagnet device 10 includes a firstcoil 101, a second coil 102, a stator 14, and a mover 15. That is tosay, in this embodiment, the second coil 102 is provided separately fromthe first coil 101. When the first coil 101 is energized, theelectromagnet device 10 has the mover 15 attracted toward the stator 14by a magnetic field generated by the first coil 101, thereby moving themover 15 upward.

In this embodiment, the electromagnet device 10 includes not only thefirst coil 101, the second coil 102, the stator 14, and the mover 15 butalso a yoke 13, a shaft 16, a holder 17, a contact pressure spring 18,and a return spring 19 as well. The electromagnet device 10 furtherincludes a cylindrical body and a coil bobbin. Note that the structureof the electromagnet device 10 is illustrated in a simplified form inFIG. 2 and illustration of the cylindrical body and the coil bobbin isomitted from FIG. 2. The same statement applies to FIGS. 3, 7, 8, 10,and 11 as well.

The stator 14 is a fixed iron core formed in the shape of a cylinderprotruding downward from a central region of the lower surface of theupper plate of the yoke 13 (from the bottom wall of the container 3 onthe drawings). The upper end portion of the stator 14 is secured to theupper plate of the yoke 13.

The mover 15 is a moving iron core also formed in the shape of acylinder. The mover 15 is arranged under the stator 14 such that theupper end face of the mover 15 faces the lower end face of the stator14. The mover 15 is configured to be movable in the upward/downwarddirection. Specifically, the mover 15 moves back and forth between afirst position where the upper end face thereof is out of contact withthe lower end face of the stator 14 (see FIG. 2) and a second positionwhere the upper end face thereof is in contact with the lower end faceof the stator 14 (see FIG. 3).

The first coil 101 is arranged under the container 3 such that itscenter axis is aligned with the upward/downward direction. The stator 14and the mover 15 are arranged inside the first coil 101. One end of thefirst coil 101 is electrically connected to a first switch 41 and theother end of the first coil 101 is electrically connected to a DC powersupply 71. The first coil 101 is formed by winding an electricallyconductive wire around a coil bobbin made of a synthetic resin. The DCpower supply 71 may have any configuration for supplying a DC current tothe first coil 101 and may include a DC/DC converter circuit or an AC/DCconverter circuit, for example.

In this embodiment, the first switch 41 forms part of a driver circuit 4for driving the first coil 101. The first switch 41 is controlled by anexternal circuit to have its ON/OFF states switched, thereby opening andclosing an electrical path connecting the first coil 101 to the DC powersupply 71. Specifically, when the first switch 41 is in ON state, adirect current flows from the DC power supply 71 into the first coil101, thereby energizing the first coil 101 (i.e., driving the first coil101). On the other hand, when the first switch 41 is in OFF state, thesupply of the direct current from the DC power supply 71 to the firstcoil 101 is suspended, thereby canceling the energized state of thefirst coil 101.

The second coil 102 is arranged inside the first coil 101 such that itscenter axis is aligned with the upward/downward direction. The mover 15is arranged inside the second coil 102. A demagnetization circuit 5 iselectrically connected to both ends of the second coil 102. The secondcoil 102 is formed by winding an electrically conductive wire around acoil bobbin made of a synthetic resin. Note that the coil bobbin for thefirst coil 101 and the coil bobbin for the second coil 102 are differentfrom each other.

The demagnetization circuit 5 is implemented as a series circuit of acapacitor 51 and a resistor 52. The capacitor 51 and the resistor 52form, along with the second coil 102, a series resonant circuit. Inother words, the demagnetization circuit 5 includes the capacitor 51that forms, along with the second coil 102, a resonant circuit. In thisembodiment, an alternating current is allowed to flow through the secondcoil 102 by utilizing the resonance between the second coil 102 and thedemagnetization circuit 5 (including the capacitor 51 and the resistor52). That is to say, the demagnetization circuit 5 supplies thealternating current to the second coil 102. The operation of thedemagnetization circuit 5 will be described in detail later in the“(2.2) Demagnetization operation” section.

The yoke 13 is arranged to surround the first coil 101. The yoke 13forms, along with the stator 14 and the mover 15, a magnetic circuit,through which a magnetic flux φ1 (see FIG. 3), produced when the firstcoil 101 is energized, passes. In other words, the magnetic flux φ1generated by the first coil 101 passes through the yoke 13. Thus, theyoke 13, the stator 14, and the mover 15 are all made of a magneticmaterial (such as a ferromagnetic body). As described above, the upperplate of the yoke 13 forms part of the bottom wall of the container 3.

The shaft 16 is made of a non-magnetic material. The shaft 16 is formedin the shape of a round rod extending in the upward/downward direction.The shaft 16 transmits the driving force, generated by the electromagnetdevice 10, to the contact device 1 provided over the electromagnetdevice 10. The shaft 16 passes through the inside of the contactpressure spring 18, a through hole provided through a central region ofthe upper plate of the yoke 13, the inside of the stator 14, and theinside of the return spring 19 to have the lower end thereof fixed ontothe mover 15. The holder 17 is fixed at the upper end of the shaft 16.

The holder 17 has the shape of a rectangular cylinder, of which theright and left surfaces are both open. The holder 17 is combined withthe moving contactor 2 such that the moving contactor 2 runs through theholder 17 in the rightward/leftward direction. The contact pressurespring 18 is arranged between the bottom wall of the holder 17 and themoving contactor 2. That is to say, a middle portion in therightward/leftward direction of the moving contactor 2 is held by theholder 17. An upper end portion of the shaft 16 is fixed onto the holder17. When the first coil 101 is energized, the shaft 16 is pushed upwardas the mover 15 moves upward. Thus, the holder 17 also moves upward. Asa result of this movement, the moving contactor 2 moves upward to bringthe pair of moving contacts 21, 22 to the closed position where the pairof moving contacts 21, 22 are in contact with the pair of fixed contacts111, 121, respectively.

The contact pressure spring 18 is arranged between the lower surface ofthe moving contactor 2 and the upper surface of the bottom wall of theholder 17. The contact pressure spring 18 is a coil spring that biasesthe moving contactor 2 upward. One end of the contact pressure spring 18is connected to the lower surface of the moving contactor 2, while theother end of the contact pressure spring 18 is connected to the uppersurface of the bottom wall of the holder 17.

At least part of the return spring 19 is arranged inside the stator 14.The return spring 19 is a coil spring that biases the mover 15 downward(toward the first position). One end of the return spring 19 isconnected to the upper end face of the mover 15 and the other end of thereturn spring 19 is connected to the upper plate of the yoke 13.

The cylindrical body is formed in the shape of a bottomed cylinder withan open upper surface. The upper end portion of the cylindrical body isbonded onto the lower surface of the upper plate of the yoke 13. Thisallows the cylindrical body to restrict the direction of movement of themover 15 to the upward/downward direction and also define the firstposition of the mover 15. The cylindrical body is hermetically bondedonto the lower surface of the upper plate of the yoke 13. This allows,even when a through hole is provided through the upper plate of the yoke13, the internal space, surrounded with the housing, the flange, and theupper plate of the yoke 13, of the contact device 1 to be kept sealedhermetically.

(2) Operation

Next, it will be described briefly how the electromagnetic relay 100according to this embodiment operates.

(2.1) Basic Operation

First, a basic operation of the electromagnetic relay 100 will bedescribed. While the first switch 14 is in OFF state and the first coil101 is supplied with no electric current (i.e., not energized), nomagnetic attractive force is generated between the mover 15 and thestator 14. Thus, in such a situation, the mover 15 is located at thefirst position under the spring force applied by the return spring 19.At this time, the shaft 16 and the holder 17 have been pulled down torestrict the upward movement of the moving contactor 2. This causes thepair of moving contacts 21, 22 held by the moving contactor 2 to belocated at the open position, which is the lower end position of theirmovable range. This brings the pair of moving contacts 21, 22 out ofcontact with the pair of fixed contacts 111, 121, respectively, thusturning the contact device 1 open. In this state, the pair of fixedterminals 11, 12 are electrically nonconductive with each other.

On the other hand, when the first switch 41 is turned ON by an externalcircuit, a direct current is supplied from the DC power supply 71 to thefirst coil 101. Thus, when the first coil 101 is energized (i.e.,supplied with an electric current), magnetic attractive force isgenerated between the mover 15 and the stator 14, thus causing the mover15 to be pulled upward by overcoming the spring force applied by thereturn spring 19 to reach the second position. At this time, the shaft16 and the holder 17 are pushed upward, thus lifting the restrictionimposed by the shaft 16 and the holder 17 against the upward movement ofthe moving contactor 2. Then, the contact pressure spring 18 biases themoving contactor 2 upward, thus causing the moving contacts 21, 22 heldby the moving contactor 2 to move toward the closed position at theupper end of their movable range. This brings the pair of movingcontacts 21, 22 into contact with the pair of fixed contacts 111, 121,respectively, thus turning the contact device 1 closed. In this state,the contact device 1 is closed, and therefore, the pair of fixedterminals 11, 12 are electrically conductive with each other. In thisstate, power is supplied from the battery 61 to the load 62.

Next, when power stops being supplied from the battery 61 to the load 62due to an excessive amount of current flowing through the load 62 andits surrounding parts, for example, the external circuit turns the firstswitch 41 OFF. Then, the supply of a direct current from the DC powersupply 71 to the first coil 101 is suspended, thus making the first coil101 electrically nonconductive. In that case, the pair of movingcontacts 21, 22 goes out of contact with the pair of fixed contacts 111,121, respectively, as described above, thus turning the contact device 1open. In this state, the pair of fixed terminals 11, 12 becomeselectrically nonconductive with each other, thus suspending the supplyof power from the battery 61 to the load 62.

This allows the electromagnet device 10 to control the magneticattractive force to be applied onto the mover 15 by selectivelyenergizing the first coil 101 and to generate driving force forswitching the state of the contact device 1 from the open state to theclosed state, and vice versa, by moving the mover 15 up and down in theupward/downward direction. In other words, the mover 15 is actuated onreceiving the magnetic flux φ1 (see FIG. 3) generated when a currentflows through the first coil 101, thus moving the moving contacts 21, 22from one of the closed position or the open position (e.g., the openposition in this example) to the other position (e.g., the closedposition in this example).

(2.2) Demagnetization Operation

Next, a demagnetization operation using the second coil 102 will bedescribed with reference to FIG. 4. In FIG. 4, the “coil current”indicates the amounts of currents flowing through the first coil 101 andthe second coil 102. Specifically, the dotted line shown in FIG. 4indicates the amount of current I1 flowing through the first coil 101(hereinafter referred to as a “first current”), while the solid lineshown in FIG. 4 indicates the amount of current I2 flowing through thesecond coil 102 (hereinafter referred to as a “second current”). Thesame statement also applies to FIG. 9 to be referred to later. Also, inFIG. 4, “displacement” indicates the displacement of the mover 15.Specifically, in FIG. 4, P1 indicates that the mover 15 is located atthe first position and P2 indicates that the mover 15 is located at thesecond position.

First, at a time t1, when the first switch 41 turns ON to energize thefirst coil 101, the first current I1 flows through the first coil 101.Thus, the magnetic flux φ1 generated by the first coil 101 producesmagnetic attractive force between the mover 15 and the stator 14 tocause the mover 15 to move from the first position to the secondposition. At this time, the magnetic flux φ1 generated by the first coil101 is interlinked with the second coil 102 provided inside the yoke 13,thus causing an induced current (second current) I2 to flow through thesecond coil 102. In this case, the second current I2 is so much smallerthan the first current I1 that the magnetic repulsion produced by thesecond current I2 hardly affects the upward movement of the mover 15.

Next, at a time t2, the first switch 41 turns OFF to cancel theenergized state of the first coil 101. Then, the supply of the firstcurrent I1 to the first coil 101 is suspended. This causes the firstcoil 101 to stop generating the magnetic flux φ1. Thus, the magneticattractive force between the mover 15 and the stator 14 is lost. As aresult, the mover 15 moves from the second position to the firstposition under the spring force applied by the return spring 19.

With this regard, the mover 15 is magnetized by receiving the magneticflux φ1 generated by the first coil 101. However, even when theenergized state of the first coil 101 is canceled after that, the mover15 may still be magnetized in some cases. In the following description,the mover 15 is supposed to be have remanent magnetization when theenergize state of the first coil 101 is canceled.

When the first coil 101 stops generating the magnetic flux φ1 at thetime t2, the magnetic flux φ1 interlinked with the second coil 102changes, thus causing the induced current (second current) I2 to flowthrough the second coil 102. Also, as the mover 15 starts returning fromthe second position toward the first position at the time t2, the mover15 with the remanent magnetization moves inside the second coil 102,thus causing the induced current (second current) I2 to flow through thesecond coil 102. Then, resonance is produced between the second coil 102and the demagnetization circuit 5 (including the capacitor 51 and theresistor 52) to cause an alternating current to flow through the secondcoil 102. The alternating current flowing through the second coil 102induces the second coil 102 to alternately generate a magnetic fluxhaving the same direction as the magnetic flux φ1 generated by the firstcoil 101 and a magnetic flux having the opposite direction from themagnetic flux φ1. In other words, when the current flows through thesecond coil 102, the second coil 102 gives at least a magnetic flux, ofwhich the direction is opposite from that of the magnetic flux φ1generated by the first coil 101, to the mover 15.

As can be seen, the mover 15 is placed in a magnetic field generated bythe alternating current flowing through the second coil 102 which has adirection that changes cyclically. Therefore, the remanent magnetizationof the mover 15 decreases with the passage of time. The strength of themagnetic field generated by the second coil 102 also decreases withtime, as the electrical energy is consumed by the resistor 52.

Next, the advantages of the electromagnetic relay 100 according to thisembodiment over an electromagnetic relay as a comparative example willbe described. The electromagnetic relay according to the comparativeexample includes no second coil 102 or demagnetization circuit 5, whichis a major difference from the electromagnetic relay 100 according tothis embodiment.

In the electromagnetic relay according to the comparative example, themover may exhibit the magnetic properties shown in FIG. 5, for example.In FIG. 5, the ordinate indicates the flux density of the magnetic fluxpassing through the mover, while the abscissa indicates the strength ofthe magnetic field in which the mover is placed. In the electromagneticrelay according to the comparative example, when placed in a magneticfield generated when the first coil is energized, the mover ismagnetized (see the state A1 shown in FIG. 5). Thereafter, when theenergized state of the first coil is canceled, the magnetic fieldstrength goes zero again but magnetization remains in the mover (see thestate A2 shown in FIG. 5). While the mover has such remanentmagnetization, the mover tends to be attracted toward the stator easily,thus taking a long time to perform the operation of opening and closingthe contact device (e.g., the operation of moving the pair of movingcontacts from the closed position to the open position in this case).That is to say, in the electromagnetic relay according to thecomparative example, the remanent magnetization of the mover increasesthe chances of causing a decline in the responsivity of theopening/closing operation of the contact device.

In contrast, in the electromagnetic relay 100 according to thisembodiment, the mover 15 may exhibit the magnetic properties shown inFIG. 6, for example. In FIG. 6, the ordinate indicates the flux densityof the magnetic flux passing through the mover 15, while the abscissaindicates the strength of the magnetic field in which the mover 15 isplaced. Also, in the first and fourth quadrants shown in FIG. 6, thedirection of the magnetic field where the mover 15 is placed is the sameas the direction of the magnetic flux φ1 generated by the first coil 101which passes through the mover 15 (hereinafter referred to as a “firstdirection”). In the second and third quadrants, the direction of themagnetic field where the mover 15 is placed is opposite from the firstdirection (and will be hereinafter referred to as a “second direction”).

As in the electromagnetic relay according to the comparative example,when placed in the magnetic field generated by energizing the first coil101, the mover 15 of the electromagnetic relay 100 according to thisembodiment is also magnetized (see the state B1 shown in FIG. 6).Thereafter, when the energized state of the first coil 101 is canceled,the magnetic field strength goes zero again but magnetization remains inthe mover 15 (see the state B2 shown in FIG. 6). In the electromagneticrelay 100 according to this embodiment, however, an alternating currentflows through the second coil 102 after the state B2, thus alternatelyplacing the mover 15 in a magnetic field with the first direction and amagnetic field with the second direction. This causes the mover 15 tomake a state transition from the state B2 to the state B3, the state B4,. . . and then the state B13 in this order with the passage of time asshown in FIG. 6. Thus, the remanent magnetization of the mover 15decreases with the passage of time.

As can be seen from the foregoing description, the electromagnetic relay100 according to this embodiment achieves the advantage of reducing theremanent magnetization of the mover 15 by placing the mover 15 in themagnetic field generated by the second coil 102. This allows theelectromagnetic relay 100 according to this embodiment to achieve theadvantage of reducing the chances of the mover 15 having remanentmagnetization that would cause a decline in the responsivity in theopening and closing operations of the contact device 1, compared to theelectromagnetic relay according to the comparative example.

(3) Variations

Next, first to third variations of the exemplary embodiment describedabove will be enumerated one after another. Note that any of thevariations to be described below may be adopted in combination with theexemplary embodiment as appropriate.

(3.1) First Variation

In the electromagnetic relay 100 a according to a first variation, thesecond coil 102 is separated from the first coil 101 by a yoke 103 asshown in FIGS. 7 and 8, which is a major difference from theelectromagnetic relay 100 according to the exemplary embodimentdescribed above. Specifically, according to this variation, the yoke 103has a recess 131, which forms a space surrounding the mover 15 at thefirst position and in which the second coil 102 is arranged. Thus, inthis variation, the first coil 101 is arranged inside the spacesurrounded with the yoke 13, while the second coil 102 is arrangedoutside that space.

In this variation, when the first coil 101 is energized, the magneticflux φ1 generated by the first coil 101 tends to pass as shown in FIG. 8through the yoke 13 with smaller magnetic resistance than the spacewhere the second coil 102 is arranged. That is to say, this variationreduces the chances of the magnetic flux φ1 generated by the first coil101 being interlinked with the second coil 102, compared with theexemplary embodiment described above.

Next, it will be described briefly with reference to FIG. 9 how theelectromagnetic relay 100 a according to this variation performs ademagnetization operation. First, when energized at a time t1, the firstcoil 101 generates a magnetic flux φ1. According to this variation, themagnetic flux φ1 generated by the first coil 101 is less likely to beinterlinked with the second coil 102, and therefore, no or almost noinduced current (second current) I2 flows through the second coil 102.Likewise, when the energized state of the first coil 101 is canceled ata time t2, the magnetic flux does not change, or hardly changes, at thesecond coil 102, and therefore, no or almost no induced current (secondcurrent) I2 flows through the second coil 102. Meanwhile, as the mover15 with the remanent magnetization moves inside the second coil 102 atthe time t2, an induced current (second current) I2 flows through thesecond coil 102. In this manner, a demagnetization operation isperformed.

As can be seen, according to this variation, as the mover 15 with theremanent magnetization moves inside the second coil 102, an inducedcurrent (second current) I2 flows through the second coil 102. Thus, thesecond coil 102 is driven to reduce the remanent magnetization of themover 15. Therefore, according to this variation, the magneticattractive force hardly affects the movement of the mover 15. Inaddition, when the mover 15 has no remanent magnetization, the secondcoil 102 is less likely driven. Consequently, the electromagnetic relay100 a according to this variation achieves the advantage of reducing theremanent magnetization of the mover 15 more efficiently than theelectromagnetic relay 100 according to the exemplary embodimentdescribed above does.

(3.2) Second Variation

In an electromagnetic relay 100 b according to a second variation, thedemagnetization circuit 5 is made up of a second switch 53 and a controlcircuit 54 as shown in FIG. 10, instead of the series circuit of thecapacitor 51 and the resistor 52, which is a major difference from theelectromagnetic relay 100 according to the exemplary embodimentdescribed above. The second switch 53 is provided on an electrical pathconnecting an AC power supply 72 to the second coil 102 to open andclose the electrical path. The control circuit 54 controls the ON/OFFstates of the second switch 53. The AC power supply 72 only needs to beconfigured to supply an alternating current to the second coil 102 andmay include a DC power supply and an inverter circuit for receiving DCpower from the DC power supply and outputting AC power. The alternatingcurrent output from the AC power supply 72 may have a sinusoidal wave ora rectangular wave, whichever is appropriate.

According to this variation, when the supply of a current to the firstcoil 101 is suspended, the control circuit 54 turns the second switch 53ON. That is to say, according to this variation, a demagnetizationoperation is performed by supplying an alternating current to the secondcoil 102 while the first coil 101 is nonconductive. This implementationis realizable by having the control circuit 54 control the ON/OFF statesof the second switch 53 in association with the ON/OFF states of thefirst switch 41 of the driver circuit 4. That is to say, the controlcircuit 54 may turn the second switch 53 ON while the first switch 41 isOFF and turn the second switch 53 OFF while the first switch 41 is ON.

As can be seen, according to this variation, turning the second switch53 ON or OFF at an arbitrary timing using the control circuit 54 allowsan alternating current to be supplied to the second coil 102 at thearbitrary timing. Thus, the electromagnetic relay 100 b according tothis variation achieves the advantage of reducing the remanentmagnetization of the mover 15 at any timing. In addition, this variationalso achieves the advantage of reducing the effect of the magneticattractive force on the movement of the mover 15, compared to turningthe second switch 53 ON while the first coil 101 is energized.

(3.3) Third Variation

In an electromagnetic relay 100 c according to a third variation, thefirst coil 101 also serves as the second coil 102 as shown in FIG. 11,which is a major difference from the electromagnetic relay 100 accordingto the exemplary embodiment described above. That is to say, theelectromagnetic relay 100 c according to this variation does not includethe second coil 102 provided separately from the first coil 101. In thisvariation, the first coil 101 also serves as the second coil 102.

In this variation, the first switch 41 is replaced with a c-contactthird switch 8. A common terminal 81 of the third switch 8 iselectrically connected to one end of the first coil 101. A normally openterminal 82 of the third switch 8 is electrically connected to thecathode of the DC power supply 71 and a normally closed terminal 83thereof is electrically connected to one terminal of the demagnetizationcircuit 5 (including the capacitor 51 and the resistor 52). The otherterminal of the demagnetization circuit 5 and the anode of the DC powersupply 71 are electrically connected to the other end of the first coil101.

In this variation, while the first coil 101 is electricallynonconductive, the demagnetization circuit 5 is connected to the firstcoil 101. Connecting the first coil 101 to the DC power supply 71 bycontrolling the third switch 8 allows the first coil 101 to be switchedfrom the electrically nonconductive state to an electrically conductivestate. Thereafter, connecting the first coil 101 to the demagnetizationcircuit 5 again by controlling the third switch 8 allows the first coil101 to be switched from the electrically conductive state to theelectrically nonconductive state. At this time, if the mover 15 hasremanent magnetization, the movement of the mover 15 with remanentmagnetization inside the second coil 102 causes an induced current(second current) I2 to flow through the second coil 102, thus having ademagnetization operation performed.

As can be seen, the electromagnetic relay 100 c according to thisvariation achieves the advantage of allowing a single coil to performboth the function of the first coil 101 and the function of the secondcoil 102.

(3.4) Other Variations

Next, other variations of the exemplary embodiment described above willbe enumerated one after another. Note that the variations to bedescribed below may be adopted in combination with the exemplaryembodiment described above (including the first to third variationsthereof) as appropriate.

In the exemplary embodiment described above, the demagnetization circuit5 includes not only the capacitor 51 but also the resistor 52 as well.However, this is only an example of the present disclosure and shouldnot be construed as limiting. That is to say, the demagnetizationcircuit 5 including only the capacitor 51 may still form a resonantcircuit with the second coil 102, and therefore, may include noresistors 52.

In the exemplary embodiment described above, the demagnetization circuit5 may be either built in, or provided as an external circuit for, theelectromagnetic relay 100, whichever is appropriate.

In the first variation described above, the second coil 102 is separatedby the yoke 13 from the first coil 101 and is magnetically independentof the first coil 101. However, this is only an example of the presentdisclosure and should not be construed as limiting. That is to say, theelectromagnetic relay 100 a may be configured to make the first coil 101and the second coil 102 magnetically independent of each other by usinga member other than the yoke 13.

In the second variation described above, the demagnetization circuit 5is configured to supply an alternating current to the second coil 102 bybeing connected to the AC power supply 72. However, this is only anexample of the present disclosure and should not be construed aslimiting. Alternatively, the demagnetization circuit 5 may also beconfigured to supply a direct current to the second coil 102 by beingconnected to a DC power supply, for example.

According to the third variation described above, the demagnetizationcircuit 5 is implemented as a so-called “passive circuit” for reducingthe remanent magnetization of the mover 15 by using an induced currentgenerated by the movement of the mover 15 magnetized. However, this isonly an example of the present disclosure and should not be construed aslimiting. Alternatively, the demagnetization circuit 5 may also beimplemented as a so-called “active circuit” for reducing the remanentmagnetization of the mover 15 by using an alternating current activelysupplied from the AC power supply 72 as in the second variationdescribed above. This implementation is realizable by replacing theseries circuit of the capacitor 51 and the resistor 52 with an AC powersupply 72. In addition, according to this implementation, thedemagnetization circuit 5 is made up of the third switch 8 and a controlcircuit for the third switch 8.

In the exemplary embodiment described above, the container 3 isconfigured to hold the fixed terminals 11, 12 with the fixed terminals11, 12 partially exposed. However, this configuration is only an exampleand should not be construed as limiting. Alternatively, the container 3may house the fixed terminals 11, 12 entirely inside itself. That is tosay, the container 3 only needs to be configured to house the fixedcontacts 111, 121 and the moving contactor 2 to say the least.

Furthermore, in the exemplary embodiment described above, theelectromagnetic relay 100 is supposed to be a so-called “normally OFF”electromagnetic relay, of which the pair of moving contacts 21, 22 arelocated at the open position while the first coil 101 is not energized.However, this is only an example and should not be construed aslimiting. Alternatively, the electromagnetic relay 100 may also be anormally ON electromagnetic relay.

Furthermore, in the exemplary embodiment described above, the number ofmoving contacts held by the moving contactor 2 is two. However, this isonly an example and should not be construed as limiting. The number ofthe moving contacts held by the moving contactor 2 may also be one oreven three or more. Likewise, the number of the fixed terminals (andfixed contacts) does not have to be two but may also be one or eventhree or more.

The electromagnetic relay 100 according to the exemplary embodimentdescribed above includes the holder 17. However, this is only an exampleof the present disclosure and should not be construed as limiting.Alternatively, the electromagnetic relay 100 may have no holders. Inthat case, the moving contactor 2 is fixed at the upper end portion ofthe shaft 16. Also, the contact pressure spring 18 is arranged betweenthe lower surface of the moving contactor 2 and the upper surface of thebottom wall of the container 3.

Furthermore, in the exemplary embodiment described above, the contactdevice 1 is implemented as a plunger type contact device. Alternatively,the contact device 1 may also be implemented as a hinged contact device.

(Resume)

As can be seen from the foregoing description, an electromagnetic relay(100, 100 a, 100 b, 100 c) according to a first aspect includes a fixedcontact (111, 121), a moving contact (21, 22), an electromagnet device(10), and a second coil (102). The moving contact (21, 22) moves from aclosed position where the moving contact (21, 22) is in contact with thefixed contact (111, 121) to an open position where the moving contact(21, 22) is out of contact with the fixed contact (111, 121), and viceversa. The electromagnet device (10) includes a first coil (101) and amover (15). The mover (15) is actuated on receiving a magnetic flux (φ1)generated when a current flows through the first coil (101) to move themoving contact (21, 22) from one of the closed position or the openposition to the other position. The second coil (102) gives, when acurrent flows through the second coil (102), at least a magnetic flux,of which a direction is opposite from a direction of the magnetic flux(φ1) generated by the first coil (101), to the mover (15).

This aspect achieves the advantage of reducing the remanentmagnetization of the mover (15).

An electromagnetic relay (100, 100 a, 100 b, 100 c) according to asecond aspect, which may be implemented in conjunction with the firstaspect, further includes a demagnetization circuit (5) to supply analternating current to the second coil (102).

This aspect allows the mover (15) to be placed in a magnetic field, ofwhich the direction changes cyclically, thus achieving the advantage offacilitating reduction in the remanent magnetization of the mover (15).

In an electromagnetic relay (100, 100 a, 100 c) according to a thirdaspect, which may be implemented in conjunction with the second aspect,the demagnetization circuit (5) includes a capacitor (51) that forms aresonant circuit with the second coil (102).

This aspect achieves the advantage of reducing the remanentmagnetization of the mover (15) without providing any power supply forsupplying an alternating current.

In an electromagnetic relay (100 b) according to a fourth aspect, whichmay be implemented in conjunction with the second aspect, thedemagnetization circuit (5) includes a switch (second switch) (53) and acontrol circuit (54). The switch (53) opens and closes an electricalpath connecting the second coil (102) to an AC power supply (72). Thecontrol circuit (54) controls ON/OFF states of the switch (53).

This aspect allows an alternating current to be supplied to the secondcoil (102) at an arbitrary timing, thus achieving the advantage ofreducing the remanent magnetization of the mover (15) at an arbitrarytiming.

In an electromagnetic relay (100 b) according to a fifth aspect, whichmay be implemented in conjunction with the fourth aspect, the controlcircuit (54) turns the switch (53) ON when supply of a current to thefirst coil (101) is suspended.

This aspect achieves the advantage of reducing, compared to the case ofturning the switch (53) ON when the first coil (101) is energized, theeffect of magnetic attractive force on the movement of the mover (15).

An electromagnetic relay (100 a, 100 b) according to a sixth aspect,which may be implemented in conjunction with any one of the first tofifth aspects, further includes a yoke (13) to allow a magnetic flux(φ1) generated by the first coil (101) to pass therethrough. The secondcoil (102) is separated from the first coil (101) by the yoke (13).

This aspect reduces the chances of the magnetic flux (φ1) generated bythe first coil (101) being interlinked with the second coil (102), thusachieving the advantage of reducing the effect of the magneticattractive force on the movement of the mover (15).

In an electromagnetic relay (100, 100 a, 100 b) according to a seventhaspect, which may be implemented in conjunction with any one of thefirst to sixth aspects, the second coil (102) is provided separatelyfrom the first coil (101).

This aspect achieves the advantage of reducing the remanentmagnetization of the mover (15) using a simpler configuration comparedto using the first coil (101) as the second coil (102) as well.

Note that the constituent elements according to the second to seventhaspects are not essential constituent elements for the electromagneticrelay (100) but may be omitted as appropriate.

REFERENCE SIGNS LIST

-   -   111, 121 Fixed Contact    -   21, 22 Moving Contact    -   10 Electromagnet Device    -   101 First Coil    -   102 Second Coil    -   13 Yoke    -   15 Mover    -   5 Demagnetization Circuit    -   51 Capacitor    -   53 Second Switch (Switch)    -   54 Control Circuit    -   AC Power Supply    -   100, 100 a, 100 b, 100 c Electromagnetic Relay    -   φ1 Magnetic Flux

1. An electromagnetic relay comprising: a fixed contact; a movingcontact configured to move from a closed position where the movingcontact is in contact with the fixed contact to an open position wherethe moving contact is out of contact with the fixed contact, and viceversa; an electromagnet device including a first coil and a moverconfigured to be actuated on receiving a magnetic flux generated when acurrent flows through the first coil to move the moving contact from oneof the closed position or the open position to the other position; and asecond coil configured to give, when a current flows through the secondcoil, at least a magnetic flux, of which a direction is opposite from adirection of the magnetic flux generated by the first coil, to themover.
 2. The electromagnetic relay of claim 1, further comprising ademagnetization circuit configured to supply an alternating current tothe second coil.
 3. The electromagnetic relay of claim 2, wherein thedemagnetization circuit includes a capacitor that forms a resonantcircuit with the second coil.
 4. The electromagnetic relay of claim 2,wherein the demagnetization circuit includes: a switch configured toopen and close an electrical path connecting the second coil to an ACpower supply; and a control circuit configured to control ON/OFF statesof the switch.
 5. The electromagnetic relay of claim 4, wherein thecontrol circuit is configured to turn the switch ON when supply of acurrent to the first coil is suspended.
 6. The electromagnetic relay ofclaim 1, further comprising a yoke configured to allow a magnetic fluxgenerated by the first coil to pass therethrough, wherein the secondcoil is separated from the first coil by the yoke.
 7. Theelectromagnetic relay of claim 1, wherein the second coil is providedseparately from the first coil.